One of the challenges in cancer research is determining the molecular events occurring at the surfaces of normal and tumor cells that account for the differences in cell-cell interactions and cell growth. The purpose of this project is to develop and apply a new type of imaging technique based on the principle that cell surfaces and other components will photoemit electrons under the action of UV light. Photoelectron imaging (photoelectron microscopy or PEM) is the electron electron optical analogue of fluorescence microscopy and is capable of extending the widely use immunofluorescence approach to much higher resolution. The mechanism of image formation is different from those of transmission or scanning electron microscopy, and the information content is complementary. Advantages include a new source of contrast (photoelectron quantum yields), very high sensitivity to fine surface detail, lower specimen damage on dehydrated and frozen hydrated specimens, ability to routinely view uncoated and unstained specimens, and theoretically, single protein resolution. In the past, this NCI grant has sponsored biophysical studies on the photoelectric effect of biological macromolecules, the first successful demonstration of photoelectron imaging of organic and biological samples, and more recently, the launching of a instrument development effort to perfect a high resolution photoelectron microscope for biological studies. The aims of the current renewal are to increase the performance of the Oregon photoelectron microscope to its design limit of resolution, to complete a general theory of photoelectron imaging, and to investigate applications of this technique in cell biology. This new technology will be applied, in conjunction with established methods (TEM, immunofluorescence and biochemistry), in studies of the mechanism whereby tumor promoters cause the release of fibronectin from the surfaces of human and other fibroblasts in culture. In addition, the photoelectric behavior of DNA will be studied, with the goal of assessing the potential of photoelectron imaging to contribute to our understanding of DNA-protein and DNA-carcinogen interactions.